This invention relates to a process for preparing colloidal sols of antimony pentoxide in organic solvents (hereinafter referred to as "antimony pentoxide organosol"). More particularly, it relates to a novel process for preparing an antimony pentoxide organosol by obtaining an antimony pentoxide gel from an alkali antimonate and an inorganic acid, after aging this gel, adding an organic base and an organic acid in an organic solvent to peptize the gel, and then removing water contained therein.
The antimony pentoxide sol is used as an auxiliary of a flame retardant for plastics, fibers, etc.; as a microfiller for surface treatment for plastics, glasses, etc.; as an inorganic ion exchanger to remove a metallic ion; and the like.
At present, high concentration aqueous sol (Sb.sub.2 O.sub.5 content of 30 to 50% by weight and pH of 4 to 8) stabilized with an organic base has generally been used. However, the aqueous sol is used only with water or a hydrophilic organic solvent such as N,N-dimethylformamide (hereinafter referred to as "DMF") and alcohols, whereby its use is greatly limited.
In recent years there has been an increased in the demand for flame retardant treatment including modification of resins. This demand is met by antimony pentoxide organosols formed in hydrophilic and hydrophobic organic solvents.
As the conventional processes for preparing the antimony pentoxide organosol, there have been known a method in which anhydrous antimony trioxide or antimony trichloride is added to nitric acid and after heating, .alpha.-hydroxycarboxylic acid is added thereto, then an organic solvent such as DMF is added thereto and water is removed by evaporation (U.S. Pat. No. 3,657,179); a method in which to a monovalent or divalent or more of alcohols to be represented by ethylene glycol is added to a hydrogen halide such as hydrogen chloride, hydrophilic organic solvent such as DMF and .alpha.-hydroxycarboxylic acid to disperse antimony trioxide, and then oxidizing it with an aqueous hydrogen peroxide solution (U.S. Pat. Nos. 4,051,064 and 4,017,418); a method in which antimony pentoxide sol, which was obtained by the method of oxidizing antimony trioxide with an aqueous hydrogen peroxide solution and stabilized with amine, is dried and pulverized, and then the powder is dispersed in an organic solvent such as DMF (U.S. Pat. No. 4,026,819); or a method for preparing an aqueous sol stabilized with a combination of alkanol amine and .alpha.-hydroxycarboxylic acid, and phosphoric acid, etc. (U.S. Pat. No. 4,348,301) wherein there is disclosed that the aqueous sol obtained by this method is mutually soluble with a hydrophilic organic solvent (e.g., methanol, DMF, etc.).
The known method described above are generally limited to organic solvents which are very hydrophilic and mixible with water over wide ranges of concentration. Also, since the organoantimony pentoxides obtained by these methods contain extremely large amounts of .alpha.-hydroxycarboxylic acid (e.g., malic acid) or hydrohalogenic acid (hydrochloric acid), at flame resistant finish of the fibers, when it was added to the polymer for fibers, large possibilities such as lowering in physical properties of a polymer or corrosion of a recovery device due to particularly halogen at recovery of an organic solvent by evaporation after spinning are present.
An example of using a hydrophilic organic solvent antimony pentoxide organosol is for a flame resistant finishing of a polymer of acrylic fibers, or for microfillers in order to give a flame retardant property or increase a surface hardness to an alcohol solution of a silicone resin which has been used as a surface treatment for plastic films, glasses, etc.
In U.S. Pat. No. 4,348,301 as mentioned above, it is possible to prepare a hydrophilic organic solvent sol in combination of alkanol amine and .alpha.-hydroxycarboxylic acid, and phosphoric acid, etc., but it cannot be applied for a hydrophobic or non-aqueous organic solvent. Further, in U.S. Pat. No. 4,026,819, there is proposed a method in which an aqueous sol stabilized with an aliphatic amine, cyclic amine, etc. is prepared and dried, and the obtained powder is then dispersed in an organic solvent such as DMF to prepare an organosol. However, the organosol obtained by the method is unstable, and by this method, an organosol of a hydrophobic organic solvent such as toluene, etc. cannot be obtained.
In recent years, there are proposed methods in which antimony pentoxide is dispersed in a hydrophobic solvent by using a specific anionic surface active agent or nonionic surface active agent (Japanese Provisional Patent Publications Nos. 161729/1985, 161730/1985 and 161731/1985). However, according to these methods, since aggregation of particles are remarkable at a high concentration to form slurry or gel, it is difficult to obtain an antimony pentoxide organosol which is used a hydrophobic solvent with low viscosity and high concentration. Further, the product having high concentration obtained by the method has disadvantage that change in color will sometimes occur with a lapse of time.